Who knows more about this?


I've got this EPROM interface from a collector in Europe. On the backsides print there is "WDT - EPROM Interface HP41C".
CAT 2 shows "BSH 1A" and a lot more, but I do not know if this is the content of the installed EPROMS (I can not remove them, sorry)...


Who knows something about this? I think it's a burner, but what is the manufactor, what is the original case, ... Any infos are wellcome. Thanks


Please Matthias,
1. Immediatly protect the Eprom windows against UV.
2. There's two 2764 Eproms and may be a 2716 or 2732.
3. Are the Eproms sold on the printed board?
4. Could you disassemble the ROM?
5. Eprom Burner but not necessary for HP-41
6. ...
I use a Mountain Computer IL Eprom Burner

It looks like the EPROMS are installed in low profile screw machine type IC sockets. From the pictures it does not appear that they were programmable while in circuit. You probably had to remove them and program them externally.

It is strange that there are three of them. Most ROM boxes used two chips to generate the 10 bit wide instructions. Perhaps there was a way of loading two different ROM images and switching between them.


Two 2764's means a total of ROM images. The smaller EPROM must be a 2732, containing the U2 bits for the 4 ROMs. There is no way that these can be programmed in circuit, and from the excellent picture it shows that the EPROMS are in sockets. I would certainly follow the advice to put a label on the EPROMS to prevent UV light getting in. There is no harm in removing the EPROMS from the sockets as long as it is done very careful so the pins are not bent.

It would be interesting to get the full CAT 2 list.



EPROMS (like most chips) can be damaged by static. Even though they may still work small static discharges can affect device life and reliability.

Before removing them get some conductive foam (this is normally 1/4 inch thick, black and doesn't spring back into shape very well). Failing that get a polystyrene ceiling tile and cover it with baking foil.

Remove the devices with a small screwdriver, working them out about 1mm at a time at each end so they come out 'square'. Do this on a (dry and clean) metal kitchen sink as this will act as a good ground. Touch the metal of the sink often to discharge your body.

After removal, immediatly press into the conductive foam / baking foil. You could also simply wrap them in the baking foil but this would mean you can see what's inside.

I would certainly put something over the window to stop the data being erased (note that a flash may have alot of uv energy - so don't photograph them again unless you cover the windows up!)

There is a funny story about flash photography and telephone exchanges. Ask if you want to know.

AFN - Tom.


I'd like to hear that story! Here are couple of related stories:

One pretty well-known story is that the stepping relay, which was used in the first dial telephone systems, was invented by a man named Strowger who was one of two morticians in his town. The wife of the other mortician was the town's telephone operator, and whenever a caller asked for a mortician, she connected them to her husband!

The other story has to do with an effort to develop a recordable CD by Memorex when it was part of Tandy Corporation. One of the engineers who worked on the project later worked in my department, after Memorex gave up on the recordable CD. He told us that Memorex had the recordable media working but a photo flash would wipe out all the data.


Didn't Tandy get sued for hyping that read-write CD, driving their stock price up, then never getting it to market?


We used to use computer tape drives (7-track and 9-track -- anybody remember those?!) to record directly our radio astronomy data (we just wrote bits as fast as the drives could go: 720 kbs was about the limit). This was the late '60s.

Once, during an attempt to document the beginning of an experiment, I took a flash picture of one of the guys next to a tape drive. At the flash, the drive took off. Apparently, one of the photocells which were used to sense the tape position in the vacuum loops and provide feedback information to the take-up and supply motors interpreted my burst of light as an out-of-tape situation, which the drive then tried to "fix."


I'm not sure, I never heard of such a lawsuit. I've been trying to remember the time-frame of that project. I'm pretty sure that another project was underway about the same time - the "Digital Compact Cassette" which Philips had specified and for which Tandy designed a recording deck. That one actually shipped but I think it didn't sell. It wasn't 4mm DAT, it used a tape cassette that looked like a regular Compact Cassette but it contained a high quality tape and sound was recorded on it digitally - the way it was explained to me, just the coefficients of an FFT were recorded (I don't know if this is true). The idea was to provide something better than regular cassettes to record your CDs on ("for personal use") - but maybe not so good that it would make the record companies mad. I remember reading that as part of an agreement to allow consumerization of DAT, the record companies were going to notch out all energy at 3 kHz on commercial audio CD's, then the DAT recorder would have to refuse to record unless there was some energy there, presumably from a live source. I've wondered what that (notched CD) would sound like! The recordable CD was going to be audio only at first, assuming the data reliability wouldn't be too good, and regular CD Audio error recovery would make it good enough for audio. Then as they worked out the bugs, they would make a recordable CD-ROM computer storage peripheral. So the time frame was after CD-ROM was available. I seem to recall that it was intended to be re-writeable from the outset - maybe that was too ambitious! But whatever the technical reasons why it didn't fly, it would still have been necessary to overcome the objections of the record companies.


Been away for a few days, here's the story told to me by my electronics teacher (who used to work for the monopoly telephone company in the UK - GPO):

An new exchange was installed and running, someone wanted to take a photo of the instalation (I think for promotion or to prove the meter readings?) and had to use a flash gun as the exchange was dark. They took the photo and the exchange 'crashed' for no apparant reason. The exchange was rebooted and all was well. Sometime later another photo was taken and again the exchange crashed.

Can you guess why?

Well - the story goes that the circuit boards had EPROMs without lables. The light energy from the flash gun was NOT enough to erase them but was enough of a energy 'kick' to make the circuits malfunction (E = hf). This is one of the reasons for putting lables over the windows of the EPROM.

I can testify that when probing silicon die in open topped packages that circuit performance changes when you have light on them - I would imagine that the number of photons coming from a photo flash gun would be enough to stop a circuit working for a milisecond or so.



I can testify that when probing silicon die in open topped packages that circuit performance changes when you have light on them ...

I've heard of that too - apparently every silicon junction will behave as a photodiode.


While we're on the subject of funny telephone circuits . . .

In the pre-Internet days, our library information services company had to lease and monitor its own network of multi-drop telephone lines connecting participant libraries with a shared database.

Our Montana (or maybe it was Idaho -- the memory is getting hazy) line suddenly started falling over randomly. As was typical in these situations, we had to get in touch with the regional telephone company and have them trace the circuit, leg-by-leg, to try to isolate the problem.

In the end, it was found this particular problem was caused by a rancher grounding his electrical fence to a local telephone junction box. Apparently, every time one of his sheep brushed the fence, libraries in the region lost their connections to our online system!


WDT could have been 'Weinert Datentechnik', which is now Cynox (www.cynox.de). Perhaps there's still somebody there who knows something...



"BSH" is obviously for 'Bausparkasse Schwäbisch-Hall'. AFAIK they used Blanknuts. Pls keep this device save and sound till we meet in August. I'll show you some more about that BSH.


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